The present invention relates to an optical transmission apparatus or system having a path trace function for performing a conductive state check of a path in a synchronous optical transmission network.
An optical transmission apparatus constituting communication nodes in a synchronous optical transmission network is required to have a path trace function, in which in order to find an erroneous connection of a path (a logical route in a transmission path) caused by a provisioning erroneous setting of a maintainer and the like, a J1 byte (a lead byte) located at a path overhead (POH) of a transfer frame between the communication nodes is used to continuously transmit and receive a path trace message (in this specification, a message included in path trace data (PTD)) and perform a conductive state check of the path.
A SONET (Synchronous Optical Network) based optical transmission apparatus having a conventional path trace function transmits and receives the path trace message through the path desired to be established, in accordance with a path trace format proposed by a GR-253 Issue (Iss.)02 standard.
For this reason, a transmission side optical transmission apparatus transmits the path trace message in accordance with the path trace format. On the other hand, a reception side optical transmission apparatus needs to check that the path is normally established by, after receiving the transmitted path trace message, extracting this message in accordance with the path trace format, and judging whether or not this is the message to be received,
This SONET-based optical transmission apparatus transmits and receives the path trace message in the path trace format proposed by the GR-253Iss.02 standard shown in FIG. 1. This path trace format has any path trace message represented by a printable or displayable ASCII (American Standard Code for Information Interchange) character code corresponding to 62 bytes, and the path trace data configuration corresponding to 64 bytes of a carriage return (CR:0Dh) code and a line feed (LF:0Ah) code. In this specification, this path trace format is referred to as a SONET 64-byte format.
As regards a method of detecting the SONET 64-byte format, a method shown in FIG. 2 is proposed in Japanese Patent Laid-Open Publication No. 11-261513 (Path Trace Check Method and Apparatus: Patent Document 1).
With this method, a path overhead (POH) is firstly extracted from a transfer frame, to extract the path trace data (PTD) from a J1 byte of this path overhead. Next, the CR code is detected from the extracted path trace data. It is known that this CR code is defined at a 63-rd byte of the SONET 64-byte format. Thus, if the CR code can be detected, the first byte of the path traced at a exists two bytes backward therefrom. Hence, those corresponding to the 64 bytes can be sequentially extracted from the first byte.
However, in the GR-253Iss.03 standard, an edition of an ANSI (American National Standards Institute) T1.269-2000 standard is additionally noted. The ANSI T1.269-2000 standard proposes the path trace formats shown in FIG. 3 and FIG. 4 to aim at the SONET/SDH (Synchronous Digital Hierarchy) uniformalization of the path trace formats.
The path trace format shown in FIG. 3 has the path trace data configuration corresponding to 16 bytes of: a header byte corresponding to 1 byte; and any path trace message represented by an ITU-T recommendation T.50 character code, namely, a printable or displayable ASCII character code corresponding to 15 bytes.
In this header byte, a frame start marker “1” is inserted into MSB (Most Significant Bit), and a circulation redundancy inspection CRC-7 operation result of a previous frame is inserted into the remaining seven bits. This format is a section trace and path trace format itself in an ITU-T recommendation G.707 (SDH). Here, the format is referred to as a 16-byte frame format.
Also, the path trace format shown in FIG. 4 has the path trace data configuration corresponding to 64 bytes of: a header byte corresponding to 1 byte; and any path trace message represented by the ITU-T recommendation T.50 character code, namely, the printable or displayable ASCII character code corresponding to 63 bytes.
This header byte is provided with the frame start marker and the CRC-7 operation result of the previous frame, similarly to the 16-byte frame format. In this specification, this is referred to as a 64-byte frame format.
As mentioned above, the ANSI T1.269-2000 is proposed in the GR-253Iss.03 standard. Thus, the optical transmission apparatus having the path trace function needs to support the path trace format of the existing standard and the path trace format of the new standard.
However, the conventional optical transmission apparatus, since having a preamble that the SONET 64-byte format is detected, cannot detect the 16-byte frame format and the 64-byte frame format. Thus, this results in a problem in that a function for detecting a new format must be separately added.
Simply, it is assumed to configure the optical transmission apparatus including detection circuits corresponding to the respective path trace formats. However, with this configuration, an increase in the apparatus (circuit) scale cannot be avoided. Thus, there is a room of improvement.
Also, the conventional optical transmission apparatus cannot automatically judge which of the formats is used to transmit and receive the path trace message (path trace data). Thus, this leads to a problem in that the format to be used for the transmission reception of the path trace message between the transmission side and the reception side must be preliminarily set for the optical transmission apparatus by the intervention of the maintainer, and the like.
The following are related arts to the present invention.
[Patent Document 1]
    Japanese Patent Laid-Open Publication No. 11-261513[Patent Document 2]    Japanese Patent Laid-Open Publication No. 11-122241[Patent Document 3]    Japanese Patent Laid-Open Publication No. 2002-101121[Non-Patent Document 1]    ANSI T1. 269-2000    Document name: Information Interchange Structure and Representation of Trace Message Formats for the North American Telecommunications System    Publisher: Alliance for Telecommunications Industry Solutions American National Standards Institute, Inc.    Date of issue: May 19, 2000    URL: https://www.atis.org/atis/docstore/searchform.asp[Non-Patent Document 2]    GR-253 Iss. 03    Document Name: Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria GR-253-CORE Issue 3    Publisher: Telcordia Technologies    Date of issue: September 2000    URL: http://telecom-info.telcordia.com/site-cgi/ido/index.html